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Electromagnets/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby Tim is vacuuming and hits a magnet. His electricity shuts off and the room goes dark. TIM: Moby, did you turn on the TV? MOBY: Beep. TIM: Well, it tripped the circuit breaker! MOBY: Beep. Moby sets the circuit breaker to on in the living room. The vacuum cleaner turns back on. Tim turns the vacuum cleaner off as Moby holds up a letter for him. Tim reads from the typed letter. TIM: Dear Tim and Moby, what is an electromagnet? From, Dar. First, let's review a little bit about regular magnets. Uh, here's one. Moby hands Tim a rectangular magnet. TIM: A simple bar magnet has a north pole and a south pole. An image shows the magnet with its poles labeled N, for north pole, and S, for south pole. TIM: Extending out from these poles is an invisible area of force called a magnetic field. An animation shows the magnetic field radiating in semicircles on either side of the magnet. The semicircular field connects the north and south poles. TIM: If you put a north pole near a south pole, the two ends will attract each other. Tim holds a bar magnet in each hand with the north pole of one facing the south pole of the other. The magnets stick to each other. TIM: But put a north pole up to another north pole, or south to a south, and you feel resistance. Tim shows how two north poles of the magnets repel each other rather than sticking together. MOBY: Beep. TIM: Any metal that contains iron, like steel, will be attracted to a magnet. The bar magnet animation and its force field are shown. A block of iron appears in a circular inset. The magnet attracts paper clips that stick to it, illustrating Tim's point. TIM: Magnets occur naturally, and people have known about them for thousands of years. An animation shows a man using a shovel. A rock that contains a magnetic substance sticks to the shovel. TIM: But in the nineteenth century, scientists discovered that you could create a magnetic field by running an electric current through a wire. The electric current produces a circular magnetic field around the wire, making it an electromagnet! An animation shows how a battery that's attached to a wire on both ends produces a current running through it. The magnetic field is labeled and arrows show its circular motion around the wire. TIM: Just like with a regular magnet, the farther you move from the wire, the weaker the magnetic field. The animation shows a paper clip close to the electromagnetic field moving closer to it, while two clips that are farther away move less. MOBY: Beep. TIM: Well, increasing the amount of current flowing through the wire strengthens the magnetic field. The animation shows a bigger battery producing a stronger magnetic field on the wire. The magnetic force pulls all of the paper clips to the wire. TIM: Reversing the direction of the current changes the polarity of the field. The animation shows that when the battery's positive and negative sides are reversed, the electromagnetic field flows in the opposite direction. A bar magnet placed next to the electromagnetic field shifts from its north to its south pole. TIM: When you turn the current off, the field disappears completely. The animation shows there is no field when the battery is disconnected from the wire. The paperclips fall away. TIM: Now, a single length of wire doesn't create a very strong magnetic field. When you coil the wire, the field strengthens. Wrapping the coil around an iron core makes a solenoid, which has an even stronger field. An animation shows how a magnetic field is strengthened as Tim describes. TIM: So electromagnets are different from regular magnets in a few major ways. They can be turned on and off, their polarity can be reversed, and their strength can be controlled. Side-by-side images illustrate how electromagnetic fields can be controlled as Tim describes. MOBY: Beep. TIM: That makes them useful in lots of different technologies. For one thing, they can convert electricity into motion. An animation shows an electric motor. TIM: Electric motors create rotational motion by taking advantage of an electromagnet's reversible polarity. An animation shows the inside of an electric motor. A rotating magnet changes polarity based on the flow of current through the wire. TIM: Electric motors are used in everything from power windows to washing machines to your computer's hard drive. Images show the things Tim describes. TIM: Some devices, like electric locks, rely on the electromagnet's ability to be turned on and off. An animation shows the electromagnetic field inside of an electric lock being turned on and off. TIM: And because the strength of an electromagnet varies with the strength of the current, it makes an ideal circuit breaker. An image shows a circuit breaker panel with circuits labeled for different rooms in a house. TIM: These devices protect your home from power surges. An animation shows the electromagnetic field behind the switch of a circuit breaker. A power surge turns the on switch to off. The image cuts out suddenly. TIM: Moby, did you turn on the TV again? Category:BrainPOP Transcripts Category:BrainPOP Engineering & Technology Transcripts Category:BrainPOP Science Transcripts